Castles, gatehouses, wall towers, docks and bridges

Town plans (#103) have no keep or castle in capitals and cities, gates are gaps with posts, walls have no towers, ports have no piers and streets ford rivers. Plan a lord's keep (a walled compound in the band facing the square: hall, towers, barracks), gatehouses over the gates, towers on the wall's corners, docks on the shore of ports and bridges where streets and roads cross rivers. Needs walkable dock and bridge pieces (the server treats water as unwalkable) and probably new catalog assets (gatehouse, bridge spans).